wallet: keep batch action order when sorting with same covenant types

[rithvikvibhu]

The code in makeBatch sorts actions to put the linked covenants first:

hsd/lib/wallet/wallet.js

Lines 3741 to 3765 in 500d638

	// Sort actions so covenants that require linked inputs
	// are pushed first into the mtx input/output arrays.
	// This is a required step otherwise an unlinked
	// covenant like NONE, OPEN, or BID could shift the
	// output array out of sync with their corresponding inputs.
	actions.sort((a, b) => {
	assert(Array.isArray(a));
	assert(Array.isArray(b));
	assert(a.length);
	assert(b.length);
	switch (b[0]) {
	case 'REVEAL':
	case 'REDEEM':
	case 'UPDATE':
	case 'RENEW':
	case 'TRANSFER':
	case 'FINALIZE':
	case 'CANCEL':
	case 'REVOKE':
	return 1;
	default:
	return -1;
	}
	});

This doesn't retain the order of actions provided. To do so, returning 0 for same covenants before the switch should work (but need to be sure it doesn't break other things):

actions.sort((a, b) => {
      assert(Array.isArray(a));
      assert(Array.isArray(b));
      assert(a.length);
      assert(b.length);

      if (a[0] === b[0]) // <--
          return 0;

      switch (b[0]) {